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Nov. 13, 1923. 1,473,826

F. J. METZGER METHOD OF FIXING NITROGEN Filed Feb. 6, 1920 Alkali Mefal I. F ['arbondle or oxide carbon Ira) axl f Mixer I Nifro yemzus Gas Holder Waste Glades F6607:

Furnaw flcrubber l Combustible M/lxfure 7 Alkali Metal t Carbonjh'axz'de Carbonate er Holder 5 H C N Condenser Patented Nov. 13, 1923.

7 UNITED STATES PATENT OFFICE.

FLOYD J'. METZGER, OF NEW YORK, N. Y., 'ASSIGNOR, BY MESNE ASSIGNMENTS, TO CALIFORNIA CYANIDE COMPANY, INCORPORATED, A CORPORATION OF DELA- WARE.

METHOD OF FIXING NITROGEN.

Application filed February 6, 1920. Serial No. 356,732.

- of Fixing Nitrogen; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains, to make and use the same.

This invention relates to the production of alkali metal cyanides, and derivatives thereof such as hydrocyanic acid, and has for its object the provision of a novel and economical method of fixing atmospheric nitrogen whereby the latter is rendered available for various uses in the arts.

The fixation of nitrogen by furnacing mixtures of alkali metal carbonates, or oxides with carbon and a proportion of iron as a catalytic material and directing a stream of nitrogen or nitrogenous gases over or through the mixture has been heretofore suggested and in Letters Patent :/:/:1, 322,195 I have described such a. method in detail. The nitrogen employed is assumed to be supplied from any suitable source and in practical operations the nitrogen has heretofore been derived from air by a method of liquefaction and subsequent sep-- aration of the constituent gases of the atmosphere.

The economical production of nitrogen by liquefaction involves the operation of a large and expensive plant, which will produce nitrogen in a much greater quantity than would be useful in connection with fixation methods at the present stage of the industry and it is desirable therefore,-to devise other sources of nitrogen, thereby permitting the erection of a self-contained fixation plant without appurtenant apparatus such as is employed in recovery of nitrogen by liquefaction or otherwise.

. A method permitting the production and fixation of nitrogen in a self-contained unit is economical in first cost and in upkeep. It maybe built on relatively small capacity and additional units may be added as required to meet the demands of the trade. Finally it requires no corps of skilled operating engineers such as is essential to a liquefaction and similar plants and the power cost which is a material factor in liquefaction is reduced to a minimum.

In the fixation of nitrogen by heating mixtures of alkali metal compounds and carbon in the presence of nitrogen, it has been considered impracticable heretofore, utilize gases containing any substantial proportion of oxygen. Oxygen readily attacks the cyanide forming cyanate which ruins the product. I have discovered, however, that by employing an excess of carbon in the mixture fed to the furnace, and by operating in such a manner that the mixture while in contact with the nitrogenous gas is maintained at the reaction temperature of substantially a red heat, all difficulty resulting from oxygen is obviated. Consequently, I am able to utilize gases which havehitherto been unavailable for fixation.

In explanation of my invention it may be 5 pointed out that while cyanate is readily formed by oxidation of cyanide in the presence of oxygen, the cyanate cannot exist in the presence of carbon at a red heat. Any cyanate formed therefore, in carrying out my invention is promptly reduced to cyanide and the resulting furnace product is consequently substantially free from the cyanate. The oxygen may even be beneficial to the method described since in combining with oxygen it liberates heat which is applied directly to the mass in a most efiicient manner.

My invention contemplates the recovery of nitrogen from flue gases by the separation of carbon dioxide therefrom. As it is quite usual to heat cyanide furnaces with combustion products and since such products contain generally about of nitrogen, it will be readily appreciated that nitrogen from this source is always available and need only be separated from carbon dioxide which need not, however, be completely removed since it is incapable of decomposing cyanide at a red heat. The separation is easily accomplished by means of a suitable scrubber and the carbon dioxide which is also recovered may be used in the treatment of the cyanide containing product to release hydrocyanic acid therefrom. In the latter 60 pending application Serial No. 356,731. The

necessity of supplying fresh alkali metal.

oxide or carbonate.

The method as thus operated, is admir ably adapted to the production of cyanide and hydrocyanic acid, especially in districts where nitrogen from ordinary sources is not readily available- Even where nitroen is available the method is superior, unless the nitrogen is a byproduct and may be piped directly to the cyanide furnaces.

The economic possibilities of the novel method are, therefore, marked and many of the diflicu-lties which have heretofore hindered the development of nitrogen fixation methods are overcome.

In the accompany drawing, I have illustrated a characteristic flow sheet inwhich the steps of the method are defined.

Referring to the drawing, it will be seen that an alkali metal carbonate or oxide, carbon and iron are brought together, preferably in a mixer which ensures thorough commingling. The mass is advantageously slightly moistened inmixing, but is dried before it is introduced to the reaction chamher. A characteristic mixture may include approximately forty-two parts of sodium carbonate, fifty-six parts of coke, and a limited quantity of iron. An amount of ironequivalent to 2% of the weight of the furnace charge in theform of iron oxide is sufiicient.

The reaction chamber is preferably an inclined rotary tube and in order to ensure continued operation, should be constructed of nichrome or similar resistant material. The tube is mounted in a suitable furnace and is adapted for rotation therein. The tube is arranged so that material treated -the-rein is not subjected to nitrogenous gases, afterentering the reaction zone at a temperature lower than approximately" a red heat. To this end a plug is inserted in the end of the tube projecting through 1 the furnace wall as illustrated in Letters latent No. 1,322,195 which prevents the passage of material beyond the furnace wall.

The plug is provided with a passage for nitrogenous gases as illustrated in my cofurnace should be thoroughly heated before the mixture'is disposed in the combustionchamber ,and consequently large, quantities.

of combustion gases are available-before the reaction commences. Producer gas may be employed as a combustible, although other heating agents are available.

A typical example of the combustion products include 80% nitrogen, 17% carbon dioxide .and 3% oxygen. Such products after preferably passing through an econo mizer, where the combustible mixture is pre heated before entering the furnace, are treated. in a gas washer to separate the carbon dioxide, leaving a residual gas, approximately 96% of nitrogen, which is suitable for use in the reaction chamber.

lVhen the furnace has reached the required temperature, a supply of nitrogenous gas has been accumulated in a gas holder, fromwhich it is supplied to the reaction chamber. The mixture is then introduced to the reaction chamber and nitrogenous gas is fed thereto in required quantity until the reaction is complete, more nitrogenous gas being accumulated at the same time through the continued operation of the washer. Then the treatment is completed, the furnace product is removed and a new batch of the mixture is introduced to the reaction chamber, the method being thereby substantially continuous. There is, of course, a large excess of furnace gases and only such portion as is needed to produce-the required nitrogenous gas is scrubbed.

The furnace product contains varying amounts of cyanide, characteristic samples varying from 20 to 30%, the remainder being sodium carbonate and oxide, carbon and iron; The cyanide maybe leached from the mass; but preferably the furnace prodnot is subjected in a converter to the action of carbon dioxide to release hydrocyan-ic" acid, as described in my copending application Serial No. 317,440. The hydrocyanic acid may be condensed and supplied to the trade as a liquid. The cyanide is converted into sodium carbonate by the reactionand the carbonate may be returned and treated with further quantities of carbon in the reaction chamber. The carbon dioxide used is preferably that separated from the comif bustion gases.

From the foregoing description, it is apparentthat I have devised a methodv of fixing nitrogen which is entirely independent of the usual commercial sourcesof nitrogen. A plant for carrying out the process maythus be erected at any point favorable to disposal of the product, provided only that fuel and sodium carbonate are available. The plant may be constructed in any desired size without regard to economic conditions affecting the operation of nitrogenproducin plants; and consequently relatively smal units may; be constructed and duplicated as the demandv for the product increases. This is a very material factor in the introduction of nitrogen fixation products, the field for which is relatively undeveloped and is subject therefore, to gradual expansion as further uses for the product are developed.

I claim:

1. A method of fixing nitrogen, which comprises heating a mixture containing an alkali metal compound and carbon with nitrogen in a reaction chamber by means of combustion gases, separating carbon dioxide from said gases, and utilizing the carbon dioxide substantially free from nitrogen to liberate hydrocyanic acid from the solid product of the reaction.

2. A method of fixing nitrogen which comprises, heating a mixture containing an alkali metal compound and carbon in a reaction chamber by means of combustion gases, separating carbon dioxide from said gases, passing the residual nitrogenous gas through said reaction chamber in contact with said mixture and subjecting the solid product of the reaction to the action of said carbon dioxide substantially free from nitrogen to liberate hydrocyanic acid.

3. A method of fixing nitrogen which comprises, heating a mixture containing an alkali metal compound and carbon in a reaction chamber by means of combustion gases, separating carbon dioxide from said gases, passing the residual nitrogenous gas through said reaction chamber in contact with said mixture, subjecting the solid product of the reaction to the action of said carbon dioxide substantially free from nitrogen to liberate hydrocyanic acid and recover alkali metal carbonate and treating the recovered alkali metal carbonate with additional quantities of carbon in said reaction chamber.

4. A method of fixing nitrogen, which comprises treating a mixture containing an alkali metal compound and carbon successively while in the solid phase with nitrogenous gases and carbon dioxide substantiall free from nitrogen, employing combustion gases to heat the mixture during contact of the nitrogenous gases therewith, and recovering nitrogenous gases and carbon dioxide from the combustion gases for use in the successive treatments.

In testimony whereof I aflix my signature.

FLOYD J. METZGE'R. 

